1. Field of Invention
The invention relates to a device for measuring fluorescence excited by light in at least one layer containing a fluorescing material, and to the use thereof for measuring fluid materials which effect fluorescence quenching in at least one of the fluorescing layers.
Measuring methods and measuring devices customarily used to date have the disadvantage that the ratio of fluorescent light to the light required to excite the fluorescence is very low, with the result that a separation is required and, consequently, a miniaturization, which is necessary for many applications, has so far been ruled out.
Further known solutions do not achieve satisfactory separation between the exciting light and the fluorescent light.
To counter this, use has so far been made of an expensive, complicated optical design which requires many optical elements, which are also cost intensive, the result being, in particular, the appearance of problems with the miniaturization and process integration.
The known solutions also have the disadvantage that the detection of the measuring signal has proceeded relatively slowly and that furthermore, errors have occurred due to coupling drift (temperature fluctuation, mismatching, or due to modem coupling), and could be taken into account only with difficulty.
2. Description of the Related Art
DD 106 086 describes a measuring probe in which fluorescence is excited in a layer, the exciting light being directed onto the layer by a single optical fiber which surrounds, in the shape of a ring, at least one further optical fiber for fluorescent light. The fluorescent light can be measured with a detector, and the measured value thereof can be used as a measure of the content or the concentration of a material, as a consequence of fluorescence quenching. Use is made for a reference measurement of a second optical fiber which directs fluorescent light of a layer region, which is screened from the measurement medium, onto a second detector.
However, it is not possible with this solution to ensure a concrete and accurate local assignment of the detectable fluorescence intensity over the excited layer surface, something which is, however, also necessary for accurate measurements because of an imprecisely defined local excitation or a non-defined, inhomogeneous arrangement of the fluorescing material in the layer. Moreover, an absolute optical separation is necessary for a simultaneous reference measurement or further measurements for other materials.
In addition, GB 2265711 A1 describes an optical fiber sensor in which two optical fibers inclined at a specific angle to one another are to be used. In this case, one of the optical fibers serves the purpose of sending light, and the other optical fiber serves the purpose of receiving reflected light and directing it onto a suitable detector. The alignment of the two optical fibers at an angle to one another is proposed there in order to achieve enlargement of the possible detection range of reflected light, since it is possible to achieve an enlarged overlap of the light exit cone with the light entrance cone of the two optical fibers.
U.S. Pat. No. 3,992,631 describes a system and a method for carrying out fluorescence immune tests in which, inter alia, reference is made to the possibility of using different optical fibers in a bundle arrangement.
It is therefore the object of the invention to propose a device which can be of miniaturized construction and therefore be adapted flexibly to different applications and achieves a satisfactory measuring accuracy.